The Energy Systems Laboratory - Il laboratorio di Sistemi per l Energia

Transcription

1 The Energy Systems Laboratory - Il laboratorio di Sistemi per l Energia Costante M. Invernizzi Università di Brescia Dipartimento di Ingegneria Meccanica e Industriale 12 marzo 2017

2 Outline 1 An introduction: the Rankine cycles with organic working fluids 2 The thermal stability of the working fluids 3 The current experimental activity

3 The steam turbine and the Rankine cycle The steam turbines in 1900 s supplanted the steam engines 350 kw Parsons Turbine at Sardinia Street Station, London, in from: A Review of Forty Years Development in Mechanical Engineering Plant for Power Station. Proceedings of the Institution of Mechanical Engineers, The owner company of the Sardinia Street Station was the first, in London, to use a steam turbine for electric generation. The company replaced ten highspeed steam engines after unsolvable disputes with the residents, complaining about the noise and vibrations of the engines. From the end of the nineteenth century, the steam engines were gradually substituted by steam turbines.

4 The steam turbine and the Rankine cycle The evolution of the steam conditions and of the thermal efficiency Temperature - Entropy Diagrams for various steam cycles. Pressures in pounds per square inch gauge - from: A Review of Forty Years Development in Mechanical Engineering Plant for Power Station. Proceedings of the Institution of Mechanical Engineers, 1939.

5 The steam turbine and the Rankine cycle The steam cycles today The flow diagram of an actual coal power plant. Net power plant: 400 MW. Net efficiency plant: 41.4%. The plant scheme is very complex and justified by its large power size.

6 The steam turbine and the Rankine cycle The steam cycles today Nuclear turbines of MW power output. from: G. Gyarmathy, Innovation and tradition in steam turbine engineerig, IMechE Part A: Journal of Power and Energy

7 The steam turbine and the Rankine cycle The steam cycles today different heat sources provide heat (steam) at very different temperatures and at different mass flow rates (capacity). Overview of live steam conditions. from: G. Gyarmathy, Innovation and tradition in steam turbine engineerig, IMechE Part A: Journal of Power and Energy

8 The Rankine cycle with organic working fluids The thermodynamic properties of steam lead to multistage, capital-intensive turbines; complex plant schemes; liquid formation during the expansion; and then the practical impossibility to obtain good exploitation efficiencies for small level of thermal power. the replacement of the steam with other working fluids (for example, hydrocarbons, refrigerants...) allow the design of efficient heat engines (1) adaptable to different heat sources with low-medium temperatures and, potentially, (2) with good performances at any designed power level.

9 The Rankine cycle with organic working fluids D Amelio solar turbine, 1934 The frontispice of the book of prof D Amelio in which he developed the design of a small solar engine (5 HP = 3.7 kw). Working fluid: C2 H5 Cl Prof Luigi D Amelio (University of Naples) was the first to employ an organic fluid in a turbine. He was also the first to consider the advantages of high molecular mass fluids to reduce the number of turbine stages and the turbine round per minute.

10 The Rankine cycle with organic working fluids The ORC today. An example LOCATION: Kirchstockach (Munich), Germany. Started: 2013; application: geothermal; description: Power only; model: Custom made; power: 5600 kw; water temperature (in/out): 138 C - by courtesy of Turboden Srl -

11 The thermal stability of the organic working fluids Today, in central Europe, about ORC-based biomass plants are operative, with electric power between kw and with temperature of the heat source (the combusted gases from the furnace) of about 1000 C. Other potential and promising applications of Rankine cycles using organic fluids are the solar power plants the industrial waste heat recovery the waste to energy sector (urban solid wastes and landfill gases) the thermal energy recovery from internal combustion engines Thermal energies made available by such sources are characterised by very different temperature levels: (1) hot water of about 30 C in OTEC plants (obviously, an extreme condition!); (2) to C in geothermal sources; (3) of about 300 C in the hot gases discharged by reciprocating enegines or gas turbines; (4) several hundreds degree in the cases of biomass or gas combustion or concentrated solar.

12 The thermal stability of the organic working fluids In principle, apart safety and environmental constraints, it is relatively simple to select the right working fluid according to the size power, but all the organic fluids incur a substantial thermochemical degradation at temperatures relatively high (say, temperatures greater than about C). Example of scaling on the first stage diaphragm of a from: DOWTHERM A - Heat Transfer Fluid - Product turbine. Technical Data, Dow Chemical Company The conversion efficiency of a heat engine strictly depends on its maximum temperature and, to minimise the heat transfer losses, the engine should be designed and operated as close as possible to the source temperature.

13 The thermal stability of the organic working fluids Our current experimental activity the measurement of the thermal stability The experimental procedure to quantify the thermal stability of a working fluid: (a) Preparation of the fluid sample (b) Evaluation of the vapor pressure of the virgin fluid (c) Thermal stress test (d) Deviations of pressure during the thermal stress tests (e) Comparison with the vapor pressure of the virgin fluid Then: the evaluation of the thermal stability of fluids is based on the analysis of: (i) the pressure deviations recorded during the thermal stress tests, (ii) the vapor pressure deviations from the reference values of the virgin fluid and (iii) the estimated decomposition rate constants. M Pasetti, C Invernizzi, P Iora - Thermal stability of working fluids for organic Rankine cycles: An improved survey method and experimental results for cyclopentane, isopentane and n-butane, Applied Thermal Engineering 73 (2014)

14 The thermal stability of the organic working fluids Our current experimental activity. Some examples. Detailed drawing of the test circuit. from: M Pasetti, C Invernizzi, P Iora - Thermal stability of working fluids for organic Rankine cycles: An improved survey method and experimental results for cyclopentane, isopentane and n-butane, Applied Thermal Engineering 73 (2014) Reference vapour pressure of cyclopentane. The vapour pressure of the virgin fluid. The measurements are compared with some vapor pressure data published in the literature.

15 The thermal stability of the organic working fluids Our current experimental activity. Some examples. Vapour pressure of a sample of cyclo-pentane before and after some decomposition tests. from: Thermal stability of organic fluids for ORC systems - Costante Mario Invernizzi, Davide Bonalumi, in, Organic Rankine Cycle (ORC) Power Systems Woodhead Publishing, September 2016 (a) Temperature and pressure trends for an hydrocarbon undergoing a massive thermal decomposition. (b) A comparison between the vapour pressure curves for the unused fluid and after its thermal decomposition.

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